Ten years after Massachusetts became the first state to allow same-sex marriage, gay and lesbian Americans can be wed in 35 states and the District of Columbia (Florida will boost that number to 36, starting Tuesday). This year, the Supreme Court may put an end to the skirmish by legalizing what progressives call “equality” and conservatives dub a “redefinition” of this cherished social institution.

The court last ruled on gay marriage in 2013 when the justices gutted much of the federal Defense of Marriage Act in United States v. Windsor and delivered a massive blow to anti-gay marriage advocates. Since then, the court has acted by not acting — in effect, doubling the number of states where gay marriage is legal, from 17 to 35, by refusing to hear a slew of appeals last year.

In November, the Cincinnati-based 6th U.S. Circuit Court of Appeals upheld gay marriage bans in four states, which will almost certainly require the high court to decide the issue once and for all.

Conservative Christians have been among the most ardent opponents of gay marriage and rights for decades. How will they respond if the Supreme Court makes gay marriage legal nationwide?

The answer, it turns out, depends on which Christian you’re speaking to.

Russell Moore, president of the Ethics and Religious Liberty Commission of the Southern Baptist Convention, has become a leading face for the next generation of Christians opposed to gay marriage. He expects the court to take up marriage this year, and is not optimistic about how they’ll rule given the Windsor decision.

NEW YORK (RNS) At a moment when American churches and politicians are warring over gay rights and same-sex marriage, each side needs every soldier it can muster. Conservatives are about to learn that one of America’s leading evangelical ethicists is defecting to the opposition.

David Gushee, a Distinguished University Professor of Christian Ethics at Mercer University, a Baptist college and divinity school in Georgia, plans to announce that he now affirms same-sex relationships, in a speech to The Reformation Project Conference, a gathering of pro-LGBT Christians in Washington, on Nov. 8.

“I do join your crusade tonight,” Gushee’s prepared remarks say, according to a draft obtained by Religion News Service. “I will henceforth oppose any form of discrimination against you. I will seek to stand in solidarity with you who have suffered the lash of countless Christian rejections. I will be your ally in every way I know how to be.”

Gushee says the journey to his current position has been a long and winding one. During the first two decades of his academic career, he maintained a traditional view of sexuality and “hardly knew a soul who was not heterosexual.” As he worked on issues such as torture and climate change, his attention was drawn to other issues — slavery, segregation, defamation of Jews, subjugating women — for which Christians once cited Scripture for their entrenched positions.

Then in 2008, his younger sister, Katey, came out as a lesbian. She is a Christian, single mother, and had been periodically hospitalized for depression and a suicide attempt. It made him realize that “traditionalist Christian teaching produces despair in just about every gay or lesbian person who must endure it.”

A former student wrote Gushee that his teachings had contributed to the painful struggle of understanding sexual identity, and scientific data suggesting that same-sex attraction is a naturally occuring form of human diversity sent him back to the Bible. Years later, he concluded that the Bible doesn’t actually teach what he previously assumed.

“It took me two decades of service as a married, straight evangelical Christian minister and ethicist to finally get here,” his speech says. “I am truly sorry that it took me so long to come into full solidarity with the Church’s own most oppressed group.”